The official guide to the toefl ibt third edition part 12 potx

TOEFL iBT Reading Correct Choices Choice 1, “Recent discoveries of fossils have helped to show the link between land mammals and cetaceans,” is correct because it represents the major idea of the entire passage. The bulk of the passage consists of a discussion of the major discoveries (Pakicetus, Basilosaurus, and Ambulocetus) that show this link. Choice 2, “The discovery of Ambulocetus natans provided evidence for a whale that lived both on land and at sea,” is correct because it is one of the major discoveries cited in the passage in support of the passage’s main point, that land mammals and cetaceans are related. Choice 5, “Fossils thought to be transitional forms between walking mammals and swimming whales were found,” is correct because like choice 1, this is a statement of the passage’s major theme as stated in paragraph 1: these fossils were “clearly intermediate, or transitional between land mammals and ceta- ceans.” The remainder of the passage discusses these discoveries. Incorrect Choices Choice 3, “The skeleton of Basilosaurus was found in what had been the Tethys Sea, an area rich in fossil evidence,” is true, but it is a minor detail and there- fore incorrect. Choice 4, “Pakicetus is the oldest fossil whale yet to be found,” is true, but it is a minor detail and therefore incorrect. Choice 6, “Ambulocetus’ hind legs were used for propulsion in the water,” is true, but it is a minor detail and therefore incorrect. 68 69 PRACTICE SET 2 DESERT FORMATION The deserts, which already occupy approximately a fourth of the Earth’s land surface, have in recent decades been increasing at an alarming pace. The expansion of desert- like conditions into areas where they did not previously exist is called desertification. It has been estimated that an additional one-fourth of the Earth’s land surface is threat- ened by this process. Desertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerated erosion of the soil by wind and water. In some cases the loose soil is blown completely away, leaving a stony surface. In other cases, the finer particles may be removed, while the sand-sized particles are accumu- lated to form mobile hills or ridges of sand. Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil’s ability to absorb substantial quantities of water. The impact of raindrops on the loose soil tends to transfer fine clay particles into the tini- est soil spaces, sealing them and producing a surface that allows very little water penetration. Water absorption is greatly reduced, consequently runoff is increased, re- sulting in accelerated erosion rates. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that a cycle of progressive surface deterioration is established. In some regions, the increase in desert areas is occurring largely as the result of a trend toward drier climatic conditions. Continued gradual global warming has pro- duced an increase in aridity for some areas over the past few thousand years. The process may be accelerated in subsequent decades if global warming resulting from air pollution seriously increases. There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes. The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel. In wet periods, the land may be able to respond to these stresses. During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity, and desertification results. Four specific activities have been identified as major contributors to the desertifi- cation processes: overcultivation, overgrazing, firewood gathering, and overirrigation. The cultivation of crops has expanded into progressively drier regions as population densities have grown. These regions are especially likely to have periods of severe dryness, so that crop failures are common. Since the raising of most crops necessi- tates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid of a plant cover and susceptible to wind and water erosion. The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. The consequences of an excessive number of livestock grazing in an area are the reduction of the vegeta- tion cover and the trampling and pulverization of the soil. This is usually followed by the drying of the soil and accelerated erosion. TOEFL iBT Reading 70 Firewood is the chief fuel used for cooking and heating in many countries. The in- creased pressures of expanding populations have led to the removal of woody plants so that many cities and towns are surrounded by large areas completely lacking in trees and shrubs. The increasing use of dried animal waste as a substitute fuel has also hurt the soil because this valuable soil conditioner and source of plant nutrients is no longer being returned to the land. The final major human cause of desertification is soil salinization resulting from overirrigation. Excess water from irrigation sinks down into the water table. If no drainage system exists, the water table rises, bringing dissolved salts to the surface. The water evaporates and the salts are left behind, creating a white crustal layer that prevents air and water from reaching the underlying soil. The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of re- versing or even slowing the process. Once the soil has been removed by erosion, only the passage of centuries or millennia will enable new soil to form. In areas where con- siderable soil still remains, though, a rigorously enforced program of land protection and cover-crop planting may make it possible to reverse the present deterioration of the surface. The deserts, which already occupy approximately a fourth of the Earth’s land sur- face, have in recent decades been increasing at an alarming pace. The expansion of desertlike conditions into areas where they did not previously exist is called deserti- fication. It has been estimated that an additional one-fourth of the Earth’s land surface is threatened by this process. Directions: Mark your answer by filling in the oval next to your choice. 1. The word threatened in the passage is closest in meaning to ɕ restricted ɕ endangered ɕ prevented ɕ rejected Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil’s ability to absorb substantial quantities of water. The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producing a surface that allows very little water penetration. Water absorption is greatly reduced, consequently runoff is increased, resulting in ac- celerated erosion rates. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that a cycle of progressive surface deterioration is established. 2. According to paragraph 3, the loss of natural vegetation has which of the follow- ing consequences for soil? ɕ Increased stony content ɕ Reduced water absorption ɕ Increased numbers of spaces in the soil ɕ Reduced water runoff P A R A G R A P H 1 P A R A G R A P H 3 Four specific activities have been identified as major contributors to the desertification processes: overcultivation, overgrazing, firewood gathering, and overirrigation. The cultivation of crops has expanded into progressively drier regions as population den- sities have grown. These regions are especially likely to have periods of severe dry- ness, so that crop failures are common. Since the raising of most crops necessitates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid of a plant cover and susceptible to wind and water erosion. There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes. The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel. In wet periods, the land may be able to respond to these stresses. During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity, and desertification results. 71 TOEFL iBT Reading 3. The word delicate in the passage is closest in meaning to ɕ fragile ɕ predictable ɕ complex ɕ valuable 4. According to paragraph 5, in dry periods, border areas have difficulty ɕ adjusting to stresses created by set- tlement ɕ retaining their fertility after desertifi- cation ɕ providing water for irrigating crops ɕ attracting populations in search of food and fuel 5. The word progressively in the passage is closest in meaning to ɕ openly ɕ impressively ɕ objectively ɕ increasingly 6. According to paragraph 6, which of the following is often associated with raising crops? ɕ Lack of proper irrigation techniques ɕ Failure to plant crops suited to the particular area ɕ Removal of the original vegetation ɕ Excessive use of dried animal waste 7. The phrase devoid of in the passage is closest in meaning to ɕ consisting of ɕ hidden by ɕ except for ɕ lacking in P A R A G R A P H 5 P A R A G R A P H 6 TOEFL iBT Reading 72 The final major human cause of desertification is soil salinization resulting from overirrigation. Excess water from irrigation sinks down into the water table. If no drainage system exists, the water table rises, bringing dissolved salts to the surface. The water evaporates and the salts are left behind, creating a white crustal layer that prevents air and water from reaching the underlying soil. 8. According to paragraph 9, the ground’s absorption of excess water is a factor in desertification because it can ɕ interfere with the irrigation of land ɕ limit the evaporation of water ɕ require more absorption of air by the soil ɕ bring salts to the surface 9. All of the following are mentioned in the passage as contributing to deser- tification EXCEPT ɕ soil erosion ɕ global warming ɕ insufficient irrigation ɕ the raising of livestock The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of revers- ing or even slowing the process. Once the soil has been removed by erosion, only the passage of centuries or millennia will enable new soil to form. In areas where consid- erable soil still remains, though, a rigorously enforced program of land protection and cover-crop planting may make it possible to reverse the present deterioration of the surface. 10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. ɕ Desertification is a significant prob- lem because it is so hard to reverse and affects large areas of land and great numbers of people. ɕ Slowing down the process of deserti- fication is difficult because of popu- lation growth that has spread over large areas of land. ɕ The spread of deserts is considered a very serious problem that can be solved only if large numbers of peo- ple in various countries are involved in the effort. ɕ Desertification is extremely hard to reverse unless the population is re- duced in the vast areas affected. 11. It can be inferred from the passage that the author most likely believes which of the following about the fu- ture of desertification? ɕ Governments will act quickly to con- trol further desertification. ɕ The factors influencing desertifica- tion occur in cycles and will change in the future. ɕ Desertification will continue to in- crease. ɕ Desertification will soon occur in all areas of the world. P A R A G R A P H 9 P A R A G R A P H 10 73 TOEFL iBT Reading 7 The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. 7 The consequences of an excessive number of livestock grazing in an area are the reduction of the vegeta- tion cover and the trampling and pulverization of the soil. 7 This is usually followed by the drying of the soil and accelerated erosion. 7 12. Look at the four squares [ 7 ] that indicate where the following sentence can be added to the passage. This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing. Where would the sentence best fit? ɕ This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing. The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural veg- etation. 7 The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulveriza- tion of the soil. 7 This is usually followed by the drying of the soil and acceler- ated erosion. 7 ɕ 7 The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing. The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulveriza- tion of the soil. 7 This is usually followed by the drying of the soil and acceler- ated erosion. 7 ɕ 7 The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. 7 The conse- quences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulverization of the soil. This eco- nomic reliance on livestock in certain regions makes large tracts of land suscep- tible to overgrazing. This is usually followed by the drying of the soil and accelerated erosion. 7 ɕ 7 The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. 7 The conse- quences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulverization of the soil. 7 This is usually followed by the drying of the soil and accelerated erosion. This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing. P A R A G R A P H 7 TOEFL iBT Reading 74 13–14. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Many factors have contributed to the great increase in desertification in recent decades. b b b Answer Choices 1. Growing human populations and the agricultural demands that come with such growth have upset the ecologi- cal balance in some areas and led to the spread of deserts. 2 As periods of severe dryness have become more common, failures of a number of different crops have in- creased. 3. Excessive numbers of cattle and the need for firewood for fuel have re- duced grasses and trees leaving the land unprotected and vulnerable. 4. Extensive irrigation with poor drainage brings salt to the surface of the soil, a process that reduces water and air absorption. 5. Animal dung enriches the soil by providing nutrients for plant growth. 6. Grasses are generally the dominant type of natural vegetation in semi- arid lands. . typically results in the loss of the soil’s ability to absorb substantial quantities of water. The impact of raindrops on the loose soil tends to transfer fine clay particles into the tini- est soil. typically results in the loss of the soil’s ability to absorb substantial quantities of water. The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces,. pressures to provide them with food and fuel. In wet periods, the land may be able to respond to these stresses. During the dry periods that are common phenomena along the desert margins, though, the